1. Field of the Disclosure
The application relates to a method utilized in a wireless communication and a communication device thereof, and more particularly, to a method of handling cell change in a wireless communication system and related communication device.
2. Description of the Prior Art
A long-term evolution (LTE) system, initiated by the third generation partnership project (3GPP), is now being regarded as a new radio interface and radio network architecture that provides a high data rate, low latency, packet optimization, and improved system capacity and coverage. In the LTE system, an evolved universal terrestrial radio access network (E-UTRAN) includes a plurality of evolved Node-Bs (eNBs) and communicates with a plurality of mobile stations, also referred as user equipments (UEs).
When the UE is powered on, the UE shall select a suitable cell based on cell selection. When the UE has completed the cell selection and has chosen a cell, the UE monitors system information of the cell. According to the system information, such as cell status or cell reservations, the UE can know if the cell is barred or reserved. When camping on the cell, the UE accepts services provided by the cell and regularly searches for a better cell according to the cell reselection criteria. If a better cell is found, that cell is selected.
Toward advanced high-speed wireless communication system, such as transmitting data in a higher peak data rate, LTE-Advanced system is standardized by the 3rd Generation Partnership Project (3GPP) as an enhancement of LTE system. LTE-Advanced system targets faster switching between power states, improves performance at the cell edge, and includes subjects, such as bandwidth extension, coordinated multipoint transmission/reception (COMP), uplink multiple input multiple output (MIMO), etc.
For bandwidth extension, carrier aggregation is introduced to the LTE-Advanced system for extension to wider bandwidth, where two or more component carriers are aggregated, for supporting wider transmission bandwidths (for example up to 100 MHz) and for spectrum aggregation. According to carrier aggregation capability, multiple component carriers are aggregated into overall wider bandwidth, where the UE can establish multiple links corresponding to the multiple component carriers for simultaneously receiving and/or transmitting.
In addition, COMP is considered for LTE-Advanced as a tool to improve coverage of high data rates, cell edge throughput, and system efficiency, which implies dynamic coordination among multiple geographical separated points. That is, when an UE is in a cell-edge region, the UE is able to receive signal from multiple cells, and the multiple cells can receive transmission of the UE.
As can be seen from the above, the UE of the LTE system supports features of receiving and transmitting on one single component carriers, whereas the UE of the LTE-Advance system supports features of simultaneously receiving and transmitting on multiple component carriers. However, the UE can perform this capability only when the serving cell of the UE also supports simultaneously reception and transmission on multiple component carriers, causing a problem related to uncoordinated capabilities between the UE and a serving cell of the UE. The “uncoordinated capabilities” herein means that a UE supports a stronger capability of reception and transmission on multiple component carriers, but the serving cell does not support this capability. The UE cannot have its data transfer up to as high efficiency as possible in the situation of “uncoordinated capabilities”.